1. Field of the Invention:
This invention relates to a photoelectric sensor comprising a light collecting system and a light receiving system.
2. Description of the Prior Art:
Since the photoelectric sensor enables a non-contact detection of persons or objects, it is used to detect any objects to be conveyed in various automated machines or conveyer lines, and any person's approach to an automatic door or the like.
FIG. 8 is a section view of a conventional photoelectric sensor, in which a convex lens is fixed in a circular opening formed on a front side of a casing. Disposed on a focal point of the convex lens is a photoelectric element comprising a light emitting element such as a light emitting diode and a light receiving element such as a phototransistor. Fixed upon an inner surface of a casing are a light driving circuit, a signal amplifying circuit, a motion indicating lamp, a variable resistor and other parts so as not to hinder an optical path between the convex lens and the photoelectric element. All of the aforesaid components are electrically connected with each other. An electric wire connected to an input terminal and an output terminal is connected to a device outside the casing.
Referring to FIG. 8, symbol A is a convex lens for light collection which is disposed on a front side of a casing B. Numeral 51 is a photoelectric element disposed on a focal point of the convex lens A. Numeral 22 is a wiring substrate, numeral 23 are various electronic parts disposed upon the wiring substrate 22, and numeral 24 is a motion indicating lamp.
Numeral 31 is a rear panel of the casing B. Symbol C is a wire for connecting the motion indicating lamp 24 and the wiring substrate 22 to each other. Such a photoelectric sensor can be installed on a certain place by means of blackets and screws.
In recent years, the structrure of the photoelectric sensor becomes more small-sized and more compact to meet user's requirements. Yet, there are the following problems hindering the manufacture of a small-sized photoelectric sensor.
Firstly, when disposing necessary parts upon the inner wall of the casing of the photoelectric sensor, an assembler is forced to insert such tools as a driver, a pinset, a soldering tool or the like into the interior of the casing. Accordingly, as the casing becomes smaller, assembling becomes more cumbersome. Thus, to make the photoelectric sensor smaller is contradictory to a better efficiency of assembling.
Secondly, since a convex lens is adapted for a light collecting means, a conically enlarged space must be formed in an optical path toward the photoelectric element. More particularly, in order to enhance the performance of the photoelectric sensor, it is desirable to increase the light incoming volume by enlarging a caliver of the convex lens and to minimize the influence of any outer disturbing light by extending a focal distance of the convex lens.
Therefore, it is needed to dispose a lens having a larger caliver and a longer focal distance, so that a larger conical space must be formed. In this regard, to make the photoelectric sensor smaller is contradictory to the betterment of optical properties.
Thirdly, handling of the conventional electric sensor is inconvenient. Since it is large-sized, it is easily touched by persons or objects, thereby an optical axis is biassed and it cause malfunction.
Finally, when some dusts or oily matters will be stuck to a body of the photoelectric sensor, cleaning is not easy.